The investigation into the poisoning of Sergei Skripal and his daughter Yulia will likely take weeks, if not months, the Metropolitan Police has announced, calling the probe "extremely challenging and complex."

"This is an extremely challenging and complex investigation and we currently have around 250 exceptionally experienced and dedicated specialist officers from the counter-terrorism network working around the clock on this case," Met Assistant Commissioner Neil Basu said on Saturday.

"They are being supported by hundreds more officers from across the police family, as well as the military and other emergency services." He went on to state that detectives are examining around 4,000 hours of CCTV footage. "They are making good progress in what is a painstaking investigation that is likely to be ongoing for weeks, if not months."

Basu's comments were published in a renewed appeal for information from anyone who may have seen Sergei Skripal's burgundy BMW 320D saloon car with the license plate HD09 WAO. It comes after an initial appeal for information was issued earlier this week.

Authorities are hoping that any information on the whereabouts of Skripal's car on March 4 will lead to further information. "We need to establish Sergei and Yulia's movements during the morning, before they headed to the town center. Did you see this car, or what you believe was this car, on the day of the incident? We are particularly keen to hear from you if you saw the car before 1:30pm. If you have information, please call the police on 101," Basu said. He also stated that anyone who has images or footage which could potentially assist the investigation can upload them to a secure UK police website.

The renewed appeal for information also includes an updated timeline of what is currently known regarding the whereabouts of the Skripals on March 4. It begins with Yulia's arrival to Heathrow Airport on a flight from Russia the previous day, and continues to document a meal at the chain restaurant Zizzi's in Salisbury on March 4, followed by emergency services being called to attend to an "extremely ill" Sergei and Yulia less than 45 minutes after they left the restaurant.